Neurostimulation systems are devices that generate electrical pulses and deliver the pulses to nerve tissue to treat a variety of disorders. Spinal cord stimulation (SCS) is an example of neurostimulation in which electrical pulses are delivered to nerve tissue in the spine for the purpose of chronic pain control. Other examples include deep brain stimulation, cortical stimulation, cochlear nerve stimulation, peripheral nerve stimulation, vagal nerve stimulation, sacral nerve stimulation, etc. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of an electrical field to spinal nervous tissue can effectively mask certain types of pain transmitted from regions of the body associated with the stimulated nerve tissue. Specifically, applying electrical energy to the spinal cord associated with regions of the body afflicted with chronic pain can induce “paresthesia” (a subjective sensation of numbness or tingling) in the afflicted bodily regions. Thereby, paresthesia can effectively mask the transmission of non-acute pain sensations to the brain.
Neurostimulation systems generally include a pulse generator and one or more leads. The pulse generator is typically implemented using a metallic housing that encloses circuitry for generating the electrical pulses, control circuitry, communication circuitry, a rechargeable battery, recharging circuitry, etc. The pulse generation circuitry is coupled to one or more stimulation leads through electrical connections provided in a “header” of the pulse generator. Stimulation leads typically include multiple wire conductors enclosed or embedded within a lead body of insulative material. Terminals and electrodes are located on the proximal and distal ends of the leads. The conductors of the leads electrically couple the terminals to the electrodes. The electrical pulses from the pulse generator are conducted through the leads and applied to patient tissue by the electrodes of the leads.
Recharging of an implanted pulse generator typically occurs by near-field coupling of a coil in the implanted pulse generator with a coil of an external charging device (which could also function as a programming device). The external charging device radiates power from its coil which induces current in the coil of the implanted pulse generator. The recharging circuitry of the implanted pulse generator rectifies the induced current and charges the battery of the implanted pulse generator (subject to various regulation circuitry).